The reducer is the core component of the concrete mixing and transporting truck, which mainly transmits the hydraulic output torque, using the reducer to the mixing cylinder through deceleration, in order to promote a stable and reliable working principle, so as to complete the mixing work of concrete. The reducer is different from the traditional mixing equipment in that it is simple in appearance and easy to maintain, and the product is adopted in large quantities in China because the system has a slow transmission speed and can operate under harsh working conditions.
1 The working principle of the mixer truck reducer
1.1 Working principle of mixer truck
The mixer truck is mainly based on the car engine as the source, which can be used as the transport power of the mixer truck and also as the variable pump in the system of the power take-off device, which not only ensures the output rotation of the motor, but also promotes the quality of the concrete itself.
The mixer truck can achieve four functions, one is the mixing function, which can ensure the quality of concrete in the mixing process. The second is the loading function, during the mixing speed of concrete, it can ensure the consistency of its direction of rotation with the transportation process. The third is the unloading function, through the pickup, hydraulic pump and reducer and other devices, its transmission with the mixing tank, can accelerate the speed of unloading. The fourth is the cleaning function, in order to prevent the concrete from sticking to the mixing cylinder, after the completion of unloading, the cleaning work should also be done.
1.2 Working principle of the reducer for mixer truck
The reducer utilized by the mixer truck is completed by the transmission structure of planetary gears, which not only creates a compact structure and a large load-bearing capacity, but also promotes a strong resistance to impact and vibration. The most typical transmission is the three-stage transmission reducer, which is a two-stage reducer composed of two side-by-side planets, and then in order to increase the transmission ratio, the fixed shaft of the other pole is input to rotate in order to complete the three-stage transmission reducer.
In the market, there are also some transmission schemes of reducers, such as one-stage NW planetary gear and one-stage NGW planetary gear transmission, which not only require a large transmission ratio, but also form a high load-bearing capacity. These transmission structures have a high load-bearing capacity with more uniform force on each gear in the process of use.
For example, the Italian Bonfiglioli reducer, which is mainly driven by the inner gear ring to transmit power to the external parts, can achieve a smaller axial size, not only can be used in the more demanding places, but also has the greater advantageous characteristics of the use of closed planetary gearbox. Therefore, closed planetary gearboxes are commonly used in construction machinery, and in order to improve the design level of our country, the relevant principles of the transmission structure should be carefully analyzed.
2 Design analysis of the reducer of concrete mixing and transportation truck
2.1 Design of gearbox transmission scheme
2.1.1 Determination of transmission ratio
To determine the transmission ratio is mainly to determine the size of the transmission ratio. During the operation of the concrete mixer truck as well as waiting for unloading, the power of the engine is taken out by using the pick-up device, and the mechanical energy of the variable pump driving the hydraulic system is converted into the quantitative motor, and finally the mixing behavior of concrete is implemented in the reducer driving the mixing cylinder device.
In order to ensure the quality of the concrete during mixing, during the transportation process, it is necessary not only to ensure the rotation of the mixing cylinder, but also to control the precision, in order to avoid waste during the operation. During this period, it is necessary to determine the motor parameters of the mixer truck, especially the working displacement, the continuous pressure formed by the work and the peak pressure. To control the speed of the hydraulic motor, generally control the mixing cylinder as well as the transmission ratio of the reducer. The calculation of the transmission ratio value is generally carried out inside the closed system, according to the relevant principles in motion and the wheel system of the transmission.
2.1.2 Determination of parameters
Three main parameters are determined.
First, the number of planetary wheels is determined, the number of planetary wheels being related to the transmission ratio. In the process of power transmission, the number of planetary wheels does not increase to obtain a larger transmission advantage, but generally remains between 2 and 5, if the number of planetary wheels selected is relatively large, it will increase the difficulty of load equalization. Moreover, the increased number of planetary wheels can also reduce the stiffness of the star frame, thus limiting the actual machining and manufacturing. Generally, to select a larger number of planetary wheels is achieved in individual low-speed stage drives.
Second, to determine the gear module, first, the planetary wheel force analysis, according to the reducer in the actual use of the situation, the analysis of the various parts of the reducer force. Then, the main points of gear strength design of planetary transmission are analyzed, and the number of cycles of stress, dynamic load coefficient and speed coefficient are mastered according to the structural characteristics of planetary transmission as well as motion characteristics. Finally, the calculation of the modulus of each gear, because the reducer is easy to impact load impact, with high strength, toughness, so in the planetary wheel, the calculation of the modulus of the wheel system should consider the tooth root bending fatigue strength.
Third, to determine the number of gear teeth, in the planetary transmission design, the number of teeth of the gear is determined mainly by analyzing the actual conditions of the transmission ratio, concentric conditions, assembly conditions and adjacent conditions.
2.1.3 Calculate the efficiency of closed planetary gear transmission
The factors affecting the efficiency of closed planetary gear transmission are mainly four points.
One is the meshing loss, which is mainly due to the power loss generated by the friction between the tooth profile.
The second is the friction loss of the bearing, because the gear is subject to fixed support on the installation shaft, easy to produce large errors.
The third is the hydraulic loss, the loss is mainly due to the gear meshing drive lubricant, in the churning and splashing generated.
The fourth is the enclosed power loss, because the enclosed power mainly exists inside the wheel system, not only with the transmission coefficient, and the friction speed of the components, friction force have a greater relationship. During the calculation of the transmission efficiency of the enclosed planetary gear, first, the transmission unit is divided, and then the transmission ratio is assigned and the transmission power on each branch is calculated.
2.1.4 Selection of the method of equalizing the load
Due to the small size and high load carrying capacity formed by planetary gearing, the main reason for this feature is that multiple planetary wheels are carrying out a shared load and forming a power split. The gears are prone to manufacturing and assembly errors during the actual transmission. The load sharing method utilized during the rotation of the gearbox is the planetary frame floating method, which does not require design support and can simplify the structure and promote a reasonable layout of multi-stage planetary gears during transmission.
2.2 Design of the oscillating mechanism
2.2.1 Oscillation form
The oscillating mechanism of the speed reducer is formed by means of spherical bearing and arc tooth oscillation. The embodiment of this structure is completed by using the connecting gear as well as the main bearing, which can not only effectively buffer the axial force but also improve the floating effect in actual work. However, the design of this structure is relatively high due to the processing cost of the drum-shaped teeth, forming a greater dependence on the equipment to be repaired and replaced separately. For the output in the form of flange swing, the structure is mainly placed on the housing of the reducer, not only the size of the reducer should be reduced, but also to form an integral part with the swing structure to reduce the number of parts. For swinging by vibration reduction, the design of this structure reserves a larger space for the mixer truck as well as other equipment, which can meet the actual needs of work.
2.2.2 Oscillating mechanism design
The design of the swing mechanism has three main forms.
One is the base ball swing, which is mainly on the support at the bottom of the reducer, and swinging action is carried out at the base with a swing ball. This type of swing can separate the reducer and swing mechanism, so if a part of the parts are damaged, not only will not affect the whole reducer, but also can facilitate maintenance. Especially for curved tooth oscillation, it is possible to form a larger angle of oscillation.
Moreover, in order to reduce the axial size of the reducer, it can also provide more space for other parts parts on the mixer truck. For the front support ball swing, it can promote the swing angle and lower the center of gravity of the mixing cylinder, but because the support is a split structure, it is solidly combined with the bolt, which is easy to cause the strength of the support and swing ball. For the ball and socket swing, the structure form saves the connection of the drum tooth and the spherical roller bearing, which not only reduces the axial size of the reducer and its weight, but also saves the cost greatly, thus the simple structure formation promotes greater convenience in the maintenance process.
As one of the most critical parts of the mixer truck, the reducer not only can mix, but also can play the role of supporting the mixing drum. Most of the mixer reducers used in China are imported, forming a greater inconvenience in the maintenance process, so in order to develop the mixer reducer in China, the design principle of this machinery and equipment should be considered, according to the actual requirements of the working conditions, not only to reduce the weight and volume of the reducer itself, but also to reduce the manufacturing cost of machinery and equipment.